Both mechanical and conventional wood pencils have, for many years, been adapted to provide an attached eraser at the end of the cylindrical pencil barrel opposite that from which the pencil lead extends. Conventional wood pencils typically are provided with a non-renewable and non-adjustable eraser attached by means of a cylindrical band and sized such that the exhaustion of the usable portion of the eraser will coincide with the life of the pencil as it is used and re-sharpened.
Mechanical pencils, on the other hand, have a virtually unlimited life by virtue of replacement pencil leads. As a result, mechanical pencils are sometimes provided with some sort of adjustable eraser mechanism and replacement erasers at the non-writing ends of the pencils. Examples of these eraser adjustment mechanisms can be found in U.S. Pat. Nos. 1,671,393; 3,072,101; 3,099,251; and 4,352,580. Each of the above listed U.S. Patents provides a unique type of adjustment mechanism to facilitate extension of additional portions of an eraser at the non-writing end as it is consumed in normal use.
U.S. Pat. No. 1,473,090, issued to Ferry, discloses a circular sleeved eraser assembly mounted on the outside of a plain lead pencil, through which the writing end of the pencil protrudes, and which places the eraser in close proximity to the lead point. A sliding of the assembly forward places the eraser segment at, and beyond the lead point of the pencil for erasure of written material.
This eraser assembly suffers several disadvantages: the assembly at the writing end unbalances the pencil, obscures the point of the pencil and the written material, is subject to relatively easy loss or mislocation, and is a meaningful obstruction to placement in a pocket. U.S. Pat. No. 4,899,419, issued to Saleen, discloses a circular, sleeved eraser assembly for use with a mechanical pencil, similar in intent to that of the Ferry patent, and suffers the same several disadvantages noted above.
U.S. Pat No. 5,127,130, issued to Copito, discloses an eraser in the shape and form of a cowling sleeve affixed to the front end of either a double acting mechanical pencil or single acting ball point pen. To use this eraser, the user must flatten the angle of the writing implement. As the eraser becomes worm, the user must increase the angle of the writing instrument while erasing, which decreases the ergonomic efficiency of the eraser. Additionally, when replacing the eraser cowling, the user could potentially loose control of the spring thereby loosing it and rendering the writing instrument inoperable.
U.S. Pat. No. 5,555,602, issued to Leamnond, discloses an eraser that is placed on the writing end of a writing instrument. At least one eraser arm extends radially outward from the finger grip section and angled forward towards the front end of the writing instrument so that a user can use the eraser by tilting and rotating the finger grip section to bring the eraser into contact with a writing surface. This type of eraser suffers the same ergonomic disadvantages as the eraser disclosed in the Copito patent in that a user must increase the angle of the writing instrument as the eraser becomes worn.
There are also several devices commercially available that do not incorporate the eraser and writing utensil into one instrument. While these devices are more ergonomic than the patented devices described above, several disadvantages still exist. One of these devices is designed so that a cylindrical eraser is tightly wrapped with paper, in a manner similar to a grease pencil. When a user desires to erase something, he or she must tear off a small portion of the paper that is wrapped around the eraser. However, when the eraser is no longer needed, it cannot be put back into the wrapper.
Another commercially available erasing device functions like a pen with a spring. The user pushes down the cap of the device, which triggers the spring causing the eraser to slide out of the tube. When this device is not in use, the user can push the cap down and slide the eraser back into the tube. While this device is an improvement over previous erasing devices, it is difficult to control the length of eraser that slides out of the tube when the cap is pushed, and the eraser is easily pushed back into the tube while in use.
A third commercially available device is an eraser inserted into a tube with a graduated slot on one side of the tube. The user moves the eraser out of the tube by pushing down on the eraser. The distance between the graduations fixes the distance the eraser slides out of the tube, and this can cause too much eraser to be out of the tube, which can lead to waste due to eraser breakage.
None of the above listed devices provide maximum convenience to the user by providing for a natural ergonomic holding position while providing total control of the eraser. Therefore, an ergonomically designed eraser that will allow users to always hold the eraser in the same easy and relaxing way while giving them total control over the length of the eraser and preventing the eraser from accidentally being pushed back into its holder is desired.